E-911 managed call routing

ABSTRACT

A method and system of local call detection and notification are provided for a communication device that communicates with an enterprise system via a secure digital voice connection and locally with the Public Switched telephone system (PSTN) via an analog line. A dialing sequence at said communication device is detected within the enterprise system for which local call routing is to be applied. Call routing is then initiated through the enterprise system and a request message is sent to the communication device that includes the dialing sequence. The request message is received within the communication device, which in response determines availability of the analog line. In the event an analog line is available the communication device sends a response message to the enterprise system for aborting call routing through the enterprise system, and locally dials said the sequence over the analog line. In the event an analog line is not available call routing continues through the enterprise system.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to European patent application number05103398.3 filed on 26 Apr. 2005, titled E-911 Managed Call Routing, theentire disclosure of which in incorporated herein for any and allpurposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to telephone systems, and moreparticularly to a method of local emergency call detection andnotification for telephone sets that communicate with a remote telephonesystem via an analog line interface module (LIM).

2. Description of the Related Art

Recent advances in communications technology have supported an increasein the number of enterprise employees and contractors who work away fromthe geographical location of the enterprise (e.g. in aSmall-Office/Home-Office (SOHO)). In such circumstances, a teleworkermay utilize a telephone that incorporates a selectable analog lineinterface module (LIM) for connection to a local central office (CO) oralternatively may communicate with the enterprise (e.g. IntegratedCommunications Platform (ICP)) via a secure digital voice connection(i.e. VoIP). Thus, the LIM device is capable of providing local E-911call routing to the connected CO. Local E-911 call routing can beinitiated by lifting the handset and selecting the analog line (possiblyselected by default), in response to which dial tone is provided by theCO and the user is permitted to dial 911.

Support of Emergency Services requires an Emergency LocationIdentification Number (ELIN) number to be sent to a Public SafetyAnswering Point (PSAP) when an emergency service number (e.g. 911) isdialed. The TIA standard prescribes al O-digit number that is insertedin the source address field on E911 trunk calls. The PSAP uses the ELINto direct emergency personnel to the location of the call. The ELIN actsas an index into the civic location database maintained at the PSAP,which in turn contains the real callback number, street address,in-building coordinates, etc. of the caller.

Thus, when a caller dials 911, a call is made to the PSAP office, andinformation regarding the phone's location is sent to the PSAP to allowemergency response professionals to locate the individual making thecall. The location information is represented by the 10 digit ELINnumber.

When the user has not selected the analog line to make an E-911 call andthe attached telephone set is connected to the enterprise, callprocessing within the ICP handles the E-911 call using existing systemE-911 call routing. However, the enterprise ICP system may be located ina different PSAP coverage area than the telephone set, or the PSAP maynot have accurate location information for the telephone set. In eitherof these cases, routing an emergency call through the enterprise systemmay result in a delayed or misdirected emergency response.

As indicated above, local E-911 call routing can be initiated by liftingthe handset and selecting the analog line. However, the user may notremember to select the analog line during an emergency. Also, someonewho is not familiar with the need to first select the analog line maydial the emergency call.

SUMMARY OF THE INVENTION

According to the present invention, a method of local emergency calldetection and notification is provided for telephone sets thatcommunicate with a remote telephone system (e.g. ICP) or locally via ananalog line interface module (LIM). Upon system detection of an E-911call, set functionality routes the call through existing system E-911call routing or through local E-911 routing on the LIM analog line,depending on line availability and user preference. Accordingly, themethod of the present invention provides support for local E-911 callrouting without user intervention, while allowing system E-911notification and associated system functionality to react to the E-911call even when local E-911 call routing is applied. The method of theinvention can also be extended to handle other dialing sequences thatwould be configured to follow local call routing through the analog linerather than system call routing, for geographic distribution and/or tollbypass, as discussed in greater detail below.

According to an embodiment of the invention, the telephone set isconfigured to recognize that a user has dialed an emergency call andautomatically apply local E-911 call routing. Safeguards are alsoprovided to prevent false detection of an E-911 call (e.g. when digitsthat match the E-911 dialing string are part of an IVR dialingsequence).

Upon detection of an E-911 call by the system, a message is sent by theenterprise system (ICP) to the set indicating that an E-911 call isbeing initiated. The message is sent to the set in addition to providingexisting E-911 support. The message is used by the set to provide E-911call indication as well as the associated dialed digits for theemergency call.

The telephone set, on receipt of the message, determines whether ananalog line is available (e.g. the set firmware uses the analog LIMwhich detects presence or absence of line voltage, where presence ofline voltage indicates an idle line while absence of voltage indicatesline busy or disconnected)). If the line is available, the telephone setaborts the system E-911 call routing (possibly by providing a hang-upindication before the call is delivered to the PSAP) and initiates localE-911 call routing. If an analog line is not available, the message isnot acted upon and/or rejected, such that system E-911 call handlingcontinues. Alternatively, the telephone set may provide a responsemessage indicating result and/or error conditions.

BRIEF DESCRIPTION OF THE DRAWING

A detailed description of the preferred embodiment is provided hereinbelow, with reference to the following drawings in which:

FIG. 1 is a block diagram of an exemplary global enterprise system (ICP)with several satellite offices and connected teleworkers, forming theoperating environment for the method according to the present invention.

FIG. 2 is a schematic representation of emergency call notificationprogression within the enterprise ICP, according to the prior art.

FIG. 3 is a message flow diagram showing a successful local emergencycall routing according to the preferred embodiment.

FIG. 4 is a message flow diagram showing a failed local emergency callrouting according to the preferred embodiment.

FIG. 5 is a message flow diagram showing a user-aborted local emergencycall routing according to the preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 depicts a communications network environment spread over a largegeographical area. One or more enterprise ICPs (such as the MN3000Integrated Communications Platform (ICP) manufactured by Mitel NetworksInc.) provide traditional PBX functionality along with advanced featuresto a plurality of centrally-located telephones (e.g. extension X2000 andanswer point X0), some of which my be digital telephone sets. However,for the purposes of the present invention, discussion is limited to setsconfigures with an analog LIM. As shown in FIG. 1, some of telephonesmay share an analog line (e.g. X2001, X2002, etc.).

As is common in the art, teleworkers may also have connections to theenterprise ICP via a Virtual Private Network (VPN) over a Wide AreaNetwork (WAN). However, as discussed above, these users are alsoconnected locally to the Public Switched telephone system (PSTN). Forexample, in FIG. 1, an ER Advisor and teleworkers in Kanata (e.g. atextensions X2005, X2006 and X4102 (via Hot-Desking)) are connected tothe enterprise ICP via a WAN but may also connect to a 911 PSAP over thePSTN. In this case, the PSAP happens to be located in the same PSAPcoverage area as the enterprise ICP. A teleworker in Arnprior (e.g. atextension X2020 and X4120 via Hot-Desking)) is connected to theenterprise ICP via the WAN but locally over the PSTN to a 911 PSAP in adifferent coverage area as than the enterprise ICP. The user in Plymouth(e.g. extension X2064) is connected to the enterprise ICP via the WANbut locally over the PSTN to a PSAP in a different coverage area thanthe enterprise ICP and also having a different emergency dialing string(e.g. 999). Finally, in the exemplary embodiment of FIG. 1, a teleworkerin Florence is connected to the enterprise ICP via the WAN but locallyover the PSTN to PSAPs in a different coverage area than the enterpriseICP and having multiple different emergency dialing strings (e.g. 114Police, 115 Fire).

In FIG. 1, the telephone at extension X2000 is indicated as beingconfigured with a Failover Only Mode. This allows selection of theanalog line by a user only when the telephone set is not registered withan ICP, thereby functioning as a fail guard in the event of network orICP failure. According to the present invention, the emergency callrouting option overrides the Failover Only Mode setting such that whenconfigured for Analog Line First (or Analog Line Only) the emergencycall always uses the attached LIM.

LIM attached telephone sets may be configured within the enterprise toselect a shared analog line within the enterprise (e.g. X2001, X2002,etc.), in the event of network or ICP failure and/or for special callhandling. For these telephones, system-only emergency call handling isappropriate.

As with the shared analog ling configuration above, LIM E911inter-working is not appropriate for a LIM attached telephone setconfigured as an answer point extension (e.g. X0). However, since systememergency call routing may restrict some telephone sets from routing tospecific PSAP destinations (Toll denial—route digits), as appropriate,the answer point extension may therefore be configured to interceptthese calls and make an emergency call on behalf of a restrictedtelephone set. The answer point telephone set is configured so as not toautomatically use local emergency call routing, but instead be allowedto use any emergency dialing string without restriction.

A LIM attached telephone set installed at a residence within the samePSAP coverage area as the enterprise (e.g. extensions X2005, X2006 andX4102 (via Hot-Desking)), allows use of the home phone line as well asteleworker functionality. In this case, the ELIN (referred to within theenterprise as CESID (Customer Emergency Services Identification))information configured for the telephone set includes the home address.Both system emergency call routing and local emergency call routingresult in connection to the same PSAP for emergency dispatch. While LIME911 inter-working affects which ELIN data (home or CESID) is used bythe PSAP, there is effectively no difference. Accordingly, emergencycall processing is preferably routed locally over the analog line andPSTN for such users.

When Hot Desking is used to allow the user to share a common extensionnumber and profile (for example, between a teleworker set (e.g. X4120)and a telephone set in the enterprise office), consistent configurationof the analog line selection key is important. An emergency calloriginated by a Hot Desk user reflects the CESID and E911 LIMconfiguration of the physical telephone set. In such situations, theanalog line is selected first.

Similarly, a LIM attached telephone set installed at a residence in adifferent PSAP coverage area (e.g. X2020) allows use of the home phoneline as well as teleworker functionality in a different city (orgeographic region). In this scenario the emergency dialing string is thesame for both PSAPs (i.e. 911). Again the CESID information configuredfor the telephone set includes the home address. However, systememergency call routing and local emergency call routing would result inconnections to different PSAPs for emergency dispatch. The call istherefore prevented in such situations from being connected to the PSAPproviding system E911 emergency dispatch to the enterprise and insteadproceeds to the local PSAP for handling, or an appropriate destinationwithin that PSAP coverage region.

For a LIM attached telephone set installed in a different country orgeographic region (e.g. extension X2064), the emergency dialing stringmay be different between the system PSAP and the local telephone setPSAP (i.e. the difference between 911 and 999). In this situation, theanalog line is used to make the emergency call to the local PSAP, andthe emergency dialing string for the local PSAP is configured in thesystem ICP to recognize an emergency call dialed at the telephone set.The system then sends a dial request message to initiate the localemergency call using the analog line, as discussed in greater detailbelow.

A LIM attached telephone set may also be installed at a residence in adifferent PSAP coverage area (e.g. extension X2076) where there aremultiple different emergency dialing strings which are also differentbetween the system PSAP and the local telephone set PSAPs (i.e. 911,114, and 115). In this situation, the analog line is used to make theemergency call to the local PSAP, and emergency dialing strings for eachdifferent PSAP are also configured in the system to recognize eachpossible emergency dialing string available at the telephone set.

According to the present invention, for those telephone sets that may beconnected both to the enterprise system ICP and a PSAP in a differentcoverage area, both the telephone set and the system ICP are configuredto recognize an emergency call dialed by the user. Thus, for theteleworkers in Arnprior, Plymouth, Florence, etc. of FIG. 1, eithersystem E-911 call routing is applied or, if the set is so configured andan analog line is available, local E-911 call routing is applied.Configuration of the emergency number in the telephone set may beaccomplished, if desired, in the firmware or in the system database andprovided to the telephone set on registration.

Upon detection of an E-911 call by the system, a message (Analog LineDial Request) is sent to the telephone set indicating an E-911 call isin the process of being established. This message is sent in addition toproviding existing E-911 system support. The existing system emergencycall routing does not proceed until a response (Analog Line DialResponse) is received from the telephone set (or a time-out occurs), toensure an emergency dial-out never results in two emergency calls placedto different PSAPs.

The Analog Line Dial Request message indicates to the telephone set thatan E-911 call has been detected (in progress) and also includes thedigits dialed up to the point of detection. The system (ICP) must beconfigured with the complete emergency dialing string for the telephoneset to dial in order to prevent predictive dialing of an emergency call.

The telephone set, on receipt of the message, determines whether ananalog line is available by communicating with the analog Line InterfaceModule (LIM), as indicated above, to determine the state of the analogline. If the analog line is available (i.e. line voltage is detected),the telephone set firmware sends the Analog Line Dial Response messageindicating the overall result of dialing proceeding (e.g. digits beingdialed on the analog line even when error conditions are reported by thetelephone set). The telephone set firmware then transitions into AnalogCall Mode (seizing the analog line, waiting for dial tone from the PSTNCentral Office (CO)). The handling of various call scenarios during thetransition into Analog Call Mode is well known in the prior art.

Following a delay for receipt of CO dial tone, the digit string providedin the Analog Line Dial Request is dialed on the analog line (providingDTMF tone) and presented to the user on the telephone set display (asdialed). The system provides local emergency notification support andproceeds to clear down the call.

As identified above, the system does not proceed with emergency callrouting until the Analog Line Dial Response message is received from thetelephone set. This may give rise to a timing issue should the user hangup on the emergency call after the system detects the emergency call andbefore the telephone set switches to analog line mode. To address thisoccurrence, when the system receives the hang up indication, the AnalogLine Dial Request message is sent to the telephone set with a dial modeof abort dialing.

Before turning to a detailed discussion of the message exchange betweenthe telephone set and ICP to enable local E911 dialing, a briefdiscussion is provided of the enterprise ICP handling of emergency callswith reference to FIG. 2.

The existing notification mechanism in Call Control for Emergency Calls(E911) is initiated after the number has been translated and the routehas been determined to be accessing a trunk that has been programmed foremergency use. For the exemplary embodiment of an MN3300/SX2000FD ICP,this is effected by entering an “E” for the “Route Type” in the CustomerData Entry (CDE) “Route Assignment” form. The detection of the emergencycall is made in a program cpars.pas.

When the emergency call is detected, a call is made to the PSAP,including the CESID information. If the Call Control has a localemergency response notification feature enabled and devices areprogrammed to receive this notification, then local notification is alsoprovided. Notification in this context is not a call, but strictly avisual and audio indication that an Emergency Call has been made.

For local emergency call handling according to the present invention,detection continues to be based on the configuration of the emergencyroute type, however the check is done earlier in the progress of thecall. This is required to send the Analog Line Dial Request notificationto the telephone set and to prevent the trunk from being seized.

As shown in FIG. 3, according to the present invention, a new sub-state(ERNMGR \ernmgr_e911_indication_substate) is introduced into the CallControl to manage LIM E911 inter-working. The CPSZEORIG function in CallControl checks for an emergency call after determining the appropriateterminator destination route from dialed digits when the caller is amultiline set.

Thus, for a multiline set, the Originating Call Process (OCP) in CallControl sends an originating call message (szeorig_prologue) to theCPSZEORIG routine in response to a caller going off-hook and dialingdigits. Upon detection of an emergency call, with an ‘E’ route marker,the CPSZEORIG routine determines the analog emergency call routingpreference and sends a message (enmgr_e911_indication_substate) to theERNMGR sub-state. If the preference is not “system only” the ERNMGRsub-state is invoked. This sub-state is responsible for determiningwhether LIM handling should be attempted, and in response sends theAnalog Line Dial Request message to the LIM attached telephone set, andwaits for the response from the telephone set (or times out). Uponreceipt of the response (Analog Line Dial Response), confirming that thecall is to be LIM-handled (system emergency call routing is blocked),the ERNMGR generates an emergency call maintenance log, provides localnotification, notifies the ER Advisor, and initiates transition to cleardown the call. When the call is not LIM-handled and system emergencycall routing is appropriate ERNMGR proceeds with normal emergency callhandling.

As would be well known to a person of ordinary skill in the art,routines are provided for encapsulating the sending and receiving of theAnalog Line Dial Request and Analog Line Dial Response (labeled Tag16#06and Tag16#86 in a successful implementation of the invention). Theformat of each message is 20 bytes in the successful embodiment and theoverall content is as follows: For TAG = 0x06 (Analog Line Dial Request)the DATA bytes are formatted as follows:  DataLen: 1 byte, number ofbytes to follow  DialMode: 1 byte, dialing mode, set by ICP: impacted bydecision to block call 0 - reserved 1 - dial always: dial regardless ofanalog line availability or on/off hook 2 - dial conditional: if analogline is available and off hook then dial 3 - cancel dialing: afterdigits are dialed send a hang up to cancel call  StringLen: 1 byte,number of bytes in the phone number to dial on the analog line DialString: n bytes, ascii digits to dial, 0-9 only For TAG = 0x86(Analog Line Dial Response) the DATA bytes are formatted as follows: DataLen: 1 byte, number of bytes to follow (=2) Result: 1 byte, theresult byte corresponding to the Analog Line Dial Request, formatted asfollows (B7 is the most-significant bit): B0 = Exception - 1 indicateshardware not installed B1 = Exception - 1 indicates hardware notconfigured B2 = Exception - 1 Indicates phone on hook B3 = Exception - 1indicates analog line in use B4 = Exception - 1 indicates invalid digitsto dial B5 = unused B6 = unused B7 = Overall Result - 0 indicates digitsdialed on analog line, 1 indicates request ignored Reserved: 1 byte,reserved for more result codes

In FIG. 4, message flow is depicted for a failed emergency call. In theevent that the emmgr_e911_indication_substate message contains invalid911 dialled digits or configuration (e.g. dialed digits too long,non-dialable digits, etc.), ENMGR either returns code to proceed withsystem Emergency Call Routing (for an Analog Line First configuration)or, for Analog Line Only configuration, the CPXCEPTN module applies busytone and sets call state in the call record to ‘waiting for analog line’(to modify the usual behaviour of CPSUS state). CPXCEPTN also displaysthe messages “LIFT HANDSET” and “SELECTANALOG LINE”. The state CPSUSthen sets a timeout duration of 30 seconds and does not change thetelephone set display. After 30 seconds, a timeout exception is applied.Alternatively, the message “NO ANALOG LINE” may be displayed, if the LIMis not installed or configured.

If the telephone set does not respond to the Analog Line Dial Requestmessage within the prescribed timeout period (e.g. 5 seconds), anemergency call maintenance log is generated to indicate ‘no response’.The ENMGR then either returns code to proceed with system Emergency CallRouting for an Analog Line First configuration or, for Analog Line Onlyconfiguration, the CPXCEPTN module applies busy tone and sets call statein the call record to ‘waiting for analog line’ (to modify the usualbehaviour of CPSUS state). CPXCEPTN also displays the messages “LIFTHANDSET” and “SELECTANALOG LINE”. The state CPSUS then sets a timeoutduration of 30 seconds and does not change the telephone set display.After 30 seconds, a timeout exception is applied. Alternatively, themessage “NO ANALOG LINE” may be displayed, if the LIM is not installedor configured.

If the telephone set responds with a failure indicated in the AnalogLine Dial Response message, then an emergency call maintenance log isgenerated for each failure condition reported. The ENMGR then eitherreturns code to proceed with system Emergency Call Routing for an AnalogLine First configuration or, for Analog Line Only configuration, theCPXCEPTN module applies busy tone and sets call state in the call recordto ‘waiting for analog line’ (to modify the usual behaviour of CPSUSstate). CPXCEPTN also displays the messages “LIFT HANDSET” and “SELECTANALOG LINE”. The state CPSUS then sets a timeout duration of 30 secondsand does not change the telephone set display. After 30 seconds, atimeout exception is applied. Alternatively, the message “NO ANALOGLINE” may be displayed, if the failure identifies a LIM is not installedor configured.

In FIG. 5, the caller goes on-hook or cancels the emergency call beforeit has been completed. The call routing is processed as discussed abovein connection with FIG. 3, except that ERNMGR sends a further AnalogLine Dial Request message to the telephone set upon receiving a ‘clear’message from the caller, for aborting local dialing. Emergency callmaintenance logs are generated to indicate a user abort, and the returncode is set as proceed to cleardown. Alternatively, the hang up islogged (absorbed) and the emergency call proceeds normally (when the LIMis capable of on-hook dialling using the analog line). This prevents anassailant from hanging up on an emergency call that is in the process ofbeing dialled on the analog line.

The primary application set forth herein is the accurate provision ofE911 services. However, a person skilled in the art will also appreciatethat the present invention can be applied whenever a call can be routedboth by the system (ICP) and locally by a set (or other device thatprovides call routing capability, such as a SIP Enabled PC). This isparticularly valuable for toll bypass when a telephone set isgeographically separated from the system. For example, when a telephoneset in Ottawa, Canada is registered with a system in London, UK anycalls made on that set would be local to the UK office. However, localanalog line access may be desired when calling for pizza delivery.Rather than requiring the user to lift the handset and select the analogline, the present invention allows the user to dial the local numberdirectly and (subject to set/system configuration) the call isautomatically routed through the local analog line rather than via thesystem. System configuration is required to distinguish between dialeddigits that represent telephone numbers local to the telephone set(which are appropriate for analog line routing) and those that areappropriate for system routing. However, this can be accomplished byconfiguring the leading (local exchange). Recognition of specificnumbers is not required although personal directory support may beutilized when available. Depending on dialing plan conflicts it may ormay not be necessary for a user to dial special prefix digit(s), i.e. 8for local calls, to distinguish between telephone numbers for system andlocal routing. Another example of toll bypass is the user in London UKdialing the number for the High Commission in Ottawa, Canada, includingthe long distance routing code. Rather than selecting a UK PSTN trunkand routing the call using long distance, the call is establishedbetween the caller and an available LIM analog line (i.e. handled withinthe system). An analog dial request message is sent to the LIM attachedtelephone set, including the High Commission dialing string local toOttawa (i.e. the long distance routing digits are omitted). The calleris thereby connected locally in Ottawa via the VPN connection alreadyestablished with the UK caller, thereby avoiding PSTN long distancecharges.

Alternative embodiments are possible within the scope of the appendedclaims. For example, configuration of the set and the system, as well asanalog line state information, can be utilized to determine whether themessage should be sent to the set. Additional information can be sent bythe system to the set (or from the set to the system) to modify how thedecision is made on which call routing to apply. State information andevents on the analog line can be exchanged between the telephone set andthe system. This information can then be utilized to determine whetherthe analog line is idle (or can be forced idle) prior to proceeding withlocal emergency call routing. As indicated above, the Analog Line DialRequest message includes a byte that indicates the dial mode. This dialmode may be one of dial always, dial conditional, dial information, etc.which the telephone set firmware interprets as appropriate. For example,when ‘dial conditional’ is indicated the emergency call is only placedusing the analog line when conditions are appropriate, while ‘dialalways’ causes the emergency call to be attempted using the analog lineeven if the line is in use (i.e. breaking an the existing call),provided the LIM supports the capability to distinguish between ‘linedisconnected’ and ‘line in use’ states.

Since numerous modifications and changes will readily occur to thoseskilled in the art, it is not desired to limit the invention to theexact construction and operation illustrated and described, andaccordingly all suitable modifications and equivalents may be resortedto, falling within the scope of the invention.

Although the present invention has been described in considerable detailwith reference to certain preferred versions thereof, other versions arepossible. Therefore, the spirit and scope of the appended claims shouldnot be limited to the description of the preferred versions containedherein.

All features disclosed in the specification, including the claims,abstract, and drawings, and all the steps in any method or processdisclosed, may be combined in any combination, except combinations whereat least some of such features and/or steps are mutually exclusive. Eachfeature disclosed in the specification, including the claims, abstract,and drawings, can be replaced by alternative features serving the same,equivalent or similar purpose, unless expressly stated otherwise. Thus,unless expressly stated otherwise, each feature disclosed is one exampleonly of a generic series of equivalent or similar features.

Any element in a claim that does not explicitly state “means” forperforming a specified function or “step” for performing a specifiedfunction should not be interpreted as a “means” or “step” clause asspecified in 35 U.S.C. §112.

1. A method of local call detection and notification for a communicationdevice that communicates with an enterprise system via a secure digitalvoice connection and locally with the Public Switched telephone system(PSTN) via an analog line, comprising: detecting within said enterprisesystem a dialing sequence at said communication device for which localcall routing is to be applied and in response initiating call routingthrough said enterprise system and sending a request message to saidcommunication device including said dialing sequence; receiving saidrequest message within the communication device and in responsedetermining availability of said analog line, and in the event saidanalog line is available sending a response message to said enterprisesystem for aborting said call routing through said enterprise system andlocally dialing said sequence over said analog line; and in the eventsaid analog line is not available continuing said call routing throughsaid enterprise system.
 2. The method of claim 1, further comprisingproviding emergency call routing within said enterprise system pendingreceipt of said response message in the event said dialing sequence isdetected to be an emergency call.
 3. The method of claim 1, furthercomprising the step of preventing completion of said call routingthrough said enterprise system pending one of either receipt of saidresponse message or a predetermined timeout period.
 4. The method ofclaim 1, wherein said step of determining availability of said analogline includes detecting presence of line voltage on said analog line. 5.The method of claim 1, further comprising the step of displaying saiddialing sequence included in said request message at said communicationdevice.
 6. The method of claim 2, further comprising the step ofgenerating an emergency call maintenance log within said enterprisesystem.
 7. The method of claim 2, further comprising the step ofnotifying an ER Advisor of said emergency call.
 8. The method of any oneof claims 1 to 7, wherein said communication device is a telephone set.9. The method of any one of claims 1 to 7, wherein said communicationdevice is a computer with telephony functions.
 10. In call control foran enterprise system with which a communication device communicates viaa secure digital voice connection, said communication device alsocommunicating locally with the Public Switched telephone system (PSTN)via an analog line, the improvement comprising: an Originating CallProcess (OCP) for generating an originating call message in response toa caller causing said communication device to go off-hook and dialing asequence of digits; a routine for determining an appropriate terminatordestination route from said sequence digits in response to generation ofsaid originating call message, and generating a further message forinitiating call routing via said enterprise system; and a call controlsub-state for receiving said further message and in response determiningwhether call routing should proceed via said analog line, sending arequest message to said communication device which, in responsedetermines availability of said analog line and in the event said analogline is available sends a response message to said enterprise system,and receiving said response message and in the event said responseindicates analog line availability then aborting said call routingthrough said enterprise system, and in the event said response indicatesunavailability of analog line then continuing said call routing throughsaid enterprise system.
 11. The improvement of claim 10, wherein saidrequest message is of the format: For TAG = 0x06 (Analog Line DialRequest) the DATA bytes are formatted as follows:  DataLen: 1 byte,number of bytes to follow  DialMode: 1 byte, dialing mode, set by ICP:impacted by decision to block call 0 - reserved 1 - dial always: dialregardless of analog line availability or on/off hook 2 - dialconditional: if analog line is available and off hook then dial 3 -cancel dialing: after digits are dialed send a hang up to cancel call StringLen: 1 byte, number of bytes in the phone number to dial on theanalog line  DialString: n bytes, ascii digits to dial, 0-9 only


12. The improvement of claim 10, wherein said response message is of theformat: Ror TAG = 0x86 (Analog Line Dial Response) the DATA bytes areformatted as follows:  DataLen: 1 byte, number of bytes to follow (=2) Result: 1 byte, the result byte corresponding to the Analog Line DialRequest, formatted as follows (B7 is the most-significant bit): B0 =Exception - 1 indicates hardware not installed B1 = Exception - 1indicates hardware not configured B2 = Exception - 1 indicates phone onhook B3 = Exception - 1 indicates analog line in use B4 = Exception - 1indicates invalid digits to dial B5 = unused B6 = unused B7 = OverallResult - 0 indicates digits dialed on analog line, 1 indicates requestignored  Reserved: 1 byte, reserved for more result codes.